At the present, a clamping head device provided with a locking mechanism is proposed, which is arranged at the front end of the electric screwdriver and the like. The locking mechanism fastens the central shaft of the inserted rotary clamp by using clamping jaws from three directions, and locks the fastening state (please refer to the No. 1 patent document for the clamping head device with the locking mechanism).
The clamping head device is provided with a clamping ring which restricts the axial direction motion relatively to the clamping head main body, and a retaining ring which can move along axial direction relatively to a pawl main body. Furthermore, a ratchet meshed toward a slack direction is arranged on the side opposite to the clamping ring and the retaining ring respectively.
Therefore, the axial movement of the retaining ring ensures that the clamping ring is meshed with the ratchet of the retaining ring, so that the rotation in the fastening unlocking direction is restricted in the state of fastening and fixation, and the fastening state can be locked.
However, the retaining ring is made to move along the axial direction, such that the clamping ring is meshed with the ratchet of the retaining ring. Therefore, when the retaining ring inadvertently moves to the direction reverse to the axial direction, the circumstance that the locking state is unlocked inadvertently may happen.
The No. 1 patent document: Japanese patent publication NO. H06-277913.